2 Passive Microwave Remote Sensing of the Ocean
31
Fig. 2.6 RFI induced wind (left) and SST (right) errors shown in descending pass difference
plots for years 1, 3, 5 and 7 of the ASMR-E mission (starting July, 2002, 2004, 2006, 2008) over
North America and Europe where the RFI has increased most in coverage and intensity over the
years. The striping is caused by the shifting orbital pattern of the most intense geostationary glint
angles
A ground RFI source off the Netherland coast has concurrently increased power
to become more prominent as seen by the small distinctive dot forming over the
years. The ground source produces SST errors of opposite sign compared to the
geostationary RFI in the region. In this small region, two prominent sources of RFI
error tend to cancel each other, potentially complicating detection and removal. The
striping visible in Fig. 2.6 is not due to any cross-swath problem with the SSTs
or wind speeds, but is due to the glint angle geometry which results in a heavily
stripped glint angle pattern caused by AMSR-E’s ground track repeat pattern every
233 orbits.
Glint angles and broadcast footprints are together highly predictive of potential
RFI bias. Therefore, to remove RFI errors from the AMSR-E SST and wind products
we calculate the signal glint angles using the longitude of the geostationary orbits.
These glint angles, together with analysis of broadcast footprints, are used to remove
retrievals with high probability of RFI error.
31
Fig. 2.6 RFI induced wind (left) and SST (right) errors shown in descending pass difference
plots for years 1, 3, 5 and 7 of the ASMR-E mission (starting July, 2002, 2004, 2006, 2008) over
North America and Europe where the RFI has increased most in coverage and intensity over the
years. The striping is caused by the shifting orbital pattern of the most intense geostationary glint
angles
A ground RFI source off the Netherland coast has concurrently increased power
to become more prominent as seen by the small distinctive dot forming over the
years. The ground source produces SST errors of opposite sign compared to the
geostationary RFI in the region. In this small region, two prominent sources of RFI
error tend to cancel each other, potentially complicating detection and removal. The
striping visible in Fig. 2.6 is not due to any cross-swath problem with the SSTs
or wind speeds, but is due to the glint angle geometry which results in a heavily
stripped glint angle pattern caused by AMSR-E’s ground track repeat pattern every
233 orbits.
Glint angles and broadcast footprints are together highly predictive of potential
RFI bias. Therefore, to remove RFI errors from the AMSR-E SST and wind products
we calculate the signal glint angles using the longitude of the geostationary orbits.
These glint angles, together with analysis of broadcast footprints, are used to remove
retrievals with high probability of RFI error.